Process for the purification of pyrethrin concentrates



Patented June 16, 1936 UNl'lED STATES PROCESS FOR THE PURIFICATION OF PYBETHRIN CONCENTBATES Herbert L. J. Heller, Washington, D. 0., and Frederick B. La Forge, Clarendon, Va, assignors to Henry A. Wallace, Secretary of Agriculture of the United States of America No Drawing. Application February 18, 1936, Serial No. 64,516

4 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) This application is made under the act of March 3, 1853, as amended by the act of April 30, 1928, and the invention herein described, if patented, may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates to the preparation of concentrates with high content of the active constituents of pyrethrum flowers. It represents a further development of the invention described in our copending patent application, Serial No. 40,288, filed September 12, 1935, and supplements the process therein described.

Although the process described in the application referred to accomplishes the removal of fats, waxes and other nontoxic byproducts from an oleoresin obtained on extraction of pyrethrum flowers with petroleum ether and generally results in a material with a content of 60-65 per cent of total active principles, the product obtained by this procedure still contains several per cent of acids of various kinds. For some purposes it is desirable to produce a concentrate of still higher pyrethrin content and which is free from acids.

Since-the pyrethrins-are esters with neutral properties, it is obvious that a solution containing them, together with other materials with acid properties in a suitable solvent, could be freed from the acid materials by treatment with an aqueous alkali solution in which the latter are soluble.

It is however practically not possible to carry out this operation because the alkali salts of the acids are of the nature of soaps and as such form emulsions in which the solution containing the pyrethrins is occluded and such emulsions separate only partly, even on very long standing.

The problem resolves itself into finding a suitable solvent capable of dissolving the pyrethrins but in which the soaps are not soluble and which does not form emulsions diiiicult to break. At the same time the nature of the solvent must be such as to permit its removal from the pyrethrin by physical or chemical means without affecting the pyrethrins. I

A liquid having these desired properties is aniline oil.

In the practice of this invention, the partly purified pyrethrin concentrate prepared as described in application, Serial No. 40,288, is dissolved in a suitable quantity of aniline, and to this solution is added a concentrated aqueous solution of potassium carbonate. The two solutions which do not mix are agitated together to insure intimate contact for several hours. Durin this process the temperature is kept at about C. by outside cooling to prevent any saponification of the pyrethrins. The reaction having been completed, the aniline solution containing the pyrethrins is separated mechanically from the aqueous solution containing the soaps resulting from the neutralization of the fatty acids. The pyrethrins are then separated from the aniline by dissolving the latter in an aqueous solution of a mineral acid maintained at a low temperature by means of ice. The pyrethrins being insoluble are separated from the acid solution by dissolving them in any low boiling solvent immiscible with water, such as petroleum ether, which solvent is subsequently removed from the pyrethrins by evaporation.

As a specific instance of the application of these processes the following more detailed description is presented.

About 140 arms. of pyrethrin concentrate obtained by the process described in application Serial No. 40,288 are dissolved in 400 cc. of freshly distilled aniline and the solution is agitated for 8 hours at 10 C. with an aqueous solution of 140 gms. of potassium carbonate in 600 cc. of water. At the end of the time specified, the two solutions are allowed to separate and the lower aqueous soap solution is drawn oii.

The aniline solution is washed by agitation with an aqueous carbonate solution and is then allowed to run slowly onto a mixture of 400 cc. of concentrated hydrochloric acid plus 400 gms. of cracked ice with constant stirring of the mixture. 'The pyrethrins which remain undissolved are extracted with petroleum ether. The petroleum ether solution is washed and dried after which the solvent is removed by evaporation leaving the purified pyrethrins in the form of a light yellow oil. The yield of material containing 70 per cent of total pyrethrins is about 90 gms.

Having described our invention we claim:

. l. I'he process of removing fatty acids from a pyrethrin concentrate which comprises dissolving the pyrethrin concentrate in aniline, treating the aniline solution with an aqueous alkali solution, removing the aqueous alkaline solution and separating the aniline from the pyrethrins by means of a mineral acid.

2. The process of removing acid materials from a pyrethrin concentrate previously freed from fats and waxes which comprises agitating the pyrethrin concentrate in aniline with an aqueous solution of an alkaline carbonate, separating the aniline solution from the aqueous solution mechanically and separating the pyrethrins irom the aniline by means of a mineral acid.

' 3. The process of removing acid materials from a pyrethrin concentrate which comprises dissolving the pyrethrin concentrate in aniline, adding a concentrated aqueous solution of potassium carbonate, agitating the two combined solutions at 10 C. for several hours, separating the aniline solution mechanically from the aqueous alkaline solution, separat'ng the pyrethrins by disa pyrethrin concentrate which comprises dissolving the pyrethrin concentrate in aniline, adding an aqueous alkaline solution to the aniline solution, agitating the two combined solutions at a reduced temperature for several hours, separating the aniline solution mechanically from the alkaline solution, separating the pyrethrins from the aniline by dissolving the latter in an aqueous solution of a mineral acid maintained at a low temperature, separatng the pyrethrins from the acid solution by dissolving them in a low boiling solvent immiscible with water and removing the solvent by evaporation.

HERBERT L. J. HALLER. FREDERICK B. LA FORGE. 

